The inch sizes are produced to the Aerospace Standard 568 published by the Society of Automotive Engineers. These inch size O Rings are designated by a dash number referenced on the AS568C chart. This standard for O-Rings contains 379 sizes and stocks them in a wide range of materials. Common stock materials for these inch size O-Rings range from Aflas, Ethylene Propylene (EPM, EPDM, EPR), Fluorocarbon (FKM, Viton Fluorel), Fluorosilicone, Highly Saturated Nitrile (HSN, HNBR), Neoprene, Nitrile (Buna-N), Perfluoroelastomers, PTFE (Teflon), Silicone, Urethane, FEP Encapsulated and more